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ROpiCAL GEOGRAPHY. 



BY / 

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SAMUEL M. SAKK, 

A Teacher in the Common Schools of Ohio. 



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CIRCLEVILrLE, OHIO : 

PUBLISHED BY THE AUTHOR. 

1887, 






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Copyright, 1887, 
By SAMUEL M. SARK 



o Of Printed and Bound by the 

UNION-HERALD PUBLISHING HOUSE, 

CIRCLEVILLE, OHIO. 



PREFACE. 

Va, 

TEXT BOOK on PHYSICAL GEOGRAPHY 

has long been needed, specially adapted to advanced classes 
in our common schools. 

It is the intention of the author to write such a text book 
on Physical Geography, but owing to the lack of means 
the first section, Astronomical Geography, now goes before 
the public asking my co-workers in the field of education 
to support me in carrying out the grand scheme of lifting 
our common schools to a higher plane of usefulness. In an 
experience of five years the author has found that our pres- 
ent system of Physical Geographies, written for high schools 
and colleges, are not adapted to the wants of our common 
schools. To meet these requirements and to encourage 
deeper investigation into the broad field of science, I place 
this little volume before the teachers of our country . 

The author holds himself responsible for any error? that 
may have crept into the work ; but if any such there be, he 



4 (PREFACE. 

will feel under lasting obligations to those who will commu- 
nicate the same to him. The work is the result of exper- 
ience and patient toil, but if it supplies the demands for 
which it was written, the author will feel greatly rewarded 
for his work . SAMUEL M. SARK. 

Circleville O., August 22, 1887. 






u VI 



INTRODUCTION. 



LESSON I. 



i. Derivation. — The word, geography, is derived from 
the Greek ge, the earth, and graphein, to write. Its literal 
signification is, therefore, a description of the earth. 

2. Sphere of Geography. ■ — Strictly speaking, geogra- 
phy includes both an account of those changes which have 
been wrought by man, and those which have been produced 
by Nature. It treats not only of the earth, but of all things 
related to the earth . In its broadest sense it includes As- 
tronomy, Geology, Mineralogy, Zcology, Meteorology, Phys_ 



6 ASTRONOMICAL GEOGRAPHY. 

ics, Botany, and various other sciences . Hence we see, 
that instead of geography being a distinct science, it is a 
collection of various sciences. 

3. Classification. — There are two-logical divisions of 
geography, political and physical. 

Political Geography treats of the earth as the dwelling 
place of man ; of the society he has organized to promote 
his own welfare ; of the government he has originated to 
suppress his crimes ; of the religion he has invented to rev- 
erence a Supreme Being ; of his manner of living etc. 

Physical Geography describes the extent and explains 
the cause of the various natural phenomena of the earth. 

4. Physical Geography is subdivided into astronom- 
ical, physiographical, meteorological, zoological and botan- 
ical geography. 

5 . Astronomical Geography is the science which con- 
siders the earth in its relation to the Universe, and in its re- 
lation to the Solar System . 

6. Physiographical Geography treats of the land 
and water belonging to the earth . 

7. Meteorological Geography is the science of the 
atmosphere and its phenomena. 

8 . Zoological Geography treats of animals and their 
distribution over the earth. 

9. Botanical Geography treats of the plants and their 
distribution. 



ASTRONOMICAL GEOGRAPHY. 7 

10. Mathematical Definitions — (a) A point has po- 
sition but no dimensions. 

(b) A line is a magnitude which has length, but no vol- 



ume. 



(c) A straight line is one that does not change its direc- 
tion throughout. 

(d) A curve line is one that changes its direction at every 
point. 

(e) Parallel lines are those, which, lying in the same 
plane, would never meet ; no matter how far they be pro- 
duced. 

(£) An angle is the parting of two lines which meet, 
(g) The point where the lines meet is called the vertex, 
(h) An angle is named from a letter placed at its vertex 
as in fig. i, which reads, the angle E or the angle F E G. 




Fig. 1. 



(i) The size of an angle depends entirely upon the dif- 
ference in direction of its sides and not at all upon the 
length of those sides. 

(j) A right angle is one formed by a straight line meet- 



8 ASTRONOMICAL GEOGRAPHY. 

ing another straight line making the adjacent angles equaL 
The first line is then said to be perpendicular to the second. 

(k) An obtuse angle is greater than a right angle. 

(1) An acute angle is less than a right angle. 




Fig. 2. 



(m) In fig. 2, A D E and E D B are right angles. A 
D C is an acute angle . C D B is an obtuse angle. 

(n) A convex surface is one that bulges out in a 
spherical form, like the outside of an egg shell. 

(o) A concave surface curves in, like the inside of an 
egg shell- 

(p) A plane has length and breadth without thickness. 

(q) A circle is a plane bounded by a curve line, every 
point of which is equally distant from a point within called 
the center, 

(r) The circumference of a circle is the line which 
bounds it. 

(s) A straight line drawn from one side of the circle to 
the other, passing through the center is called the diameter. 

(t) A straight line drawn from center to circumference 
is called the radius. 



ASTRONOMICAL GEOGRAPHY. 9 

(u) The circumference of a circle is divided into 360 
equal parts called degrees . 

(v) An angle is measured by the number of degrees 
in the arc that subtends it . 

(w) An Ellipse is a plane figure, bounded by a curve 
line, every point of which is at such distances from two 
points within, called its foci, that the sum of these distances 
is in each case the same. 

(x) The center of an ellipse is the point midway be- 
tween the foci. 

(y) The Major Axis is the longest diameter. 

(aa) The Minor Axis is the shortest diameter. 



In 


x c\ 




h—*^^^ 



Fig. 3. 

(bb) Fig. 3 represents an ellipse. 
O and X are the foci. 
D C is the major axis. 
A B is the minor axis . 



10 ASTRONOMICAL GEOGRAPHY- 

(cc) A solid has length, breadth, and thickness. 

(dd) A Sphere is a volume bounded by a curved sur- 
face, every point of which is equally distant from a point 
within called the center. 

The diameter of a sphere is a straight line passing from 
one side, through the center, to the other side. 

(ee) The Axis of a revolving sphere is the diameter 
around which it turns. 

The ends of the axis are called the poles. 

(ff) An Oblate Spheroid is a sphere flattened at the 
poles like an orange. 

(gg) A Prolate Spheroid is a sphere elongated at the 
poles like a lemon. 



, SECTION 



LEbSON II. 



1, The Universe is the name applied to the entire ma- 
terial world. 

There are truths before which man becomes humiliated 
and perplexed, although, he knows from the very nature of 
things, the absolute necessity of their existence. Among 
such are the eternal duration of time and the infinity of 
space. We live, therefore, in an expanse without limits, in 
whose bosom the universe is floating. 

2. Constituents of the Universe. — The first persons 
who studied the heavenly bodies fancied the Earth standing 
in the center of a hollow sphere ; that the stars were golden 
nails, which,seen on the concave surface, the great Architect 
of the universe had used in its construction. 

Modern science teaches us that the universe is composed 
of Nebulae, Stars, Planets, Satellites, Comets and Meteors. 

These bodies are divided into luminous and non-luminous 
bodies. Luminous bodies shine by their own light. Non 
luminous bodies shine by reflecting light of the luminous 
bodies. 



n ASTRONOMICAL GEOGRAPHY. 

3. Nebulae — It has long been a subject of debate whether 
there existed a nebulous fluid in space. When the spectro- 
scope was invented it forever ended the controversy. The 
nebulae (nebula, a cloud) are masses of glowing gas, prob- 
ably, Hidrogen and Nitrogen. 

The light of some of the nebulae, is subjected to great var- 
iations. 

They are separated from us by such enormous distances 
that light, wiiich travels at the enormous rate t 86,000 miles 
per second, requires many thousand years to reach us from 
some whose existence is revealed by the telescope . Many 
parts of the heavens having a nebulous appearance, contain 
no nebulae ; but the glowing mass consists of many stars, 
apparently, near each other, but doubtless, this appearance 
is due to the inconceivable distances they are apart from us ; 
and they are in reality as widely separated from each other, 
as the stars of our own Milky Way. Nearly all of the 
nebulae lie far beyond our stellar universe. 

4. Stars. — Stars are huge balls of matter, which, float- 
ing in the depth of space, give us light because they are 
white hot. They are visible during the night, and are 
known by their twinkling ; but during the day their light is 
extinguished by the presence of the greater light of one 
glorious star, the Sun, whose rays light up and warm the 
earth. The stars are moving rapidly through space, al- 



ASTRONOMICAL GEOGRAPHY, 13 

"though, they are apparently at rest on account of the great 
distances they are from us. 

The Sun appears to be the largest and brightest star in the 
firmament. This is because that orb is comparatively near 
ois. The apparent feebleness of the stars is due to the great 
■distances they are separated from us; the nearest being 
more than 200,000 times more distant than the sun. 

Some stars are much larger and brighter than the sun . 
As the land surveyor measurer, the distance across a river 
which he cannot cross, so, too, the astronomer spans the 
enormous distances from star to star. 

Alpha Centauri is the nearest star, the Sun excepted. It 
is about 20,000,000,000,000 miles away. This is a truth which 
in our minds can form no conception. Yet this distance is 
small when compared with the distances of the stars of the 
1 2th magnitude made visible by the telescope ; for it only 
takes light about three and a half years to reach us from 
Apha Centauri ; while if a star of the 12th magnitude 
would be at this moment destroyed, the inhabitants of the 
earth would continue to see it for 3,500 years. That is, it 
takes the light of these distant luminaries 3,500 years to 
reach us. 

A cannon ball taking the earth as its starting point, trav- 
eling at the rate of 1,320 feet per second^ would not arrive 
at Alpha Centauri in less than 2,500,000 years ; while a rail- 
road train running at the rate of 40 miles per hour, would 



H ASTRONOMICAL GEOGRAPHY. 

arrive at that star in about 55,000,000 years. These dis- 
tances are entirely to great for our conception, yet they are 
but mere points in boundless space. 

5. The Magnitude of a star depends upon its relative 
brightness. The brightest stars are known as stars of the 
first magnitude ; while the most feeble visible to the naked 
eye, are of the sixth magnitude. There are about 20 stars 
of the first magnitude ; 65, of the second ; 200, of the third; 
450, of fourth ; 1,100, of the fifth ; 4,000, of the sixth. The 
number increases largely in ascending the scale. From the 
above we see that the whole number of stars visible to the 
naked eye, is about 6,000. 

Since we see but one-half of the sky, the greatest num- 
ber visible at a time, is about 3,000. With a powerful tele- 
scope about 20,0c 0,000 stars between the first and sixteenth 
magnitude, inclusive, are visible. 

Of this number more than 18,000,000 belong to our own 
stellar universe, the Milky Way. 

6. Constellations. — The stars are arranged in groups 
called constellations and are usually named after a fabulous 
personage or some animal w 7 hich the relative position of the 
stars suggested to the mythological mind. 

7 Variations. — The light of some of the stars, as in 
the case of the nebulae, is subjected to variations which, so 
far as we now know r , occur in regular periods of time. 

The cause of these variations is unknown, but three 



ASTRONOMICAL GEOGRAPHY, 15 

theories have been advanced which are worthy of attention. 

First — It is believed that all parts of the star's photosphere, 
or surface, are not (equally luminous ; that it revolves upon 
its axis ; and, hence it is brightest when the brightest side is 
turned toward us, and darkest when the dark side meets 
our view. 

Second — It is believed that the star has one or more non- 
luminous planets revolving around it ; that these planets get 
between us and the star forming either a total or partial 
ecilpse. 

Third — It has been found that when a planet comes near 
the Sun it becomes brighter. Hence it is supposed that the 
variable has a large planet revolving around it ; and that 
that part of the star's photosphere nearest the planet will be 
brightest. 

8. Color. — The light of most of the stars is white , 
but some are red, orange, blue, green, etc. 

9. Constituents of the Stars. — We know but little 
of the elements of the stars ; however, we do know that 
their photospheres contain some elements known to us. 
Among the most widely diffused are Hidrogen, Sodium and 
Iron. The constituent elemets of the stars bear a striking 
resemblance to each other. It seems probable that each of 
these great luminaries has the same past history. At pre- 
sent, we are not prepared to conjecture about the future. 

10. The Milky Way. — We have already spoken of 



16 ASTRONOMICAL GEOGRAPHY. 

star-clusters under the head of nebuhe . The sun, all of 
the stars visible to the naked eye, and millions of telescopic 
stars form one great star-cluster, known as the Milky Way. 
A ray of light traveling at the rate of 186,000 miles per sec- 
ond, starting at one side of the Milky Way, passing through 
the center, would reach the opposite side in about 15,00a 
years ! Then leaving the last star in our cluster it would 
continue at its usual velocity, for several millions of years,, 
through empty space and at last arrive at other star-clusters,, 
some of them exceeding our own Milky Way in vastness 
of extent and numbers. Thus we see that the visible star- 
clusters, numbering about 5,000, and isolated from each 
other by inconceivable distances, are only so many milky 
ways floating in the bosom of infinite space. 



LESSON HI. 



i. The Sol, ml System. — The Solar System is situated 
in the center of that portion of the universe known as the 
Milky Way. 

2 . Constituents, The Solar System is composed of 
the sun, planets, satellites, comets, meteors and an apparent 
ring of nebulous matter called the Zodiacal Light. 

3 . The Sun is the center of the Solar System. It holds 
all the other members of the system in their respective 
places by its attraction . 



ASTRONOMICAL GEOGRAPHY. 17 

It supplies the planets with light and heat, and supports 
all animal and vegetable life on our globe . 

If we examine the Sun with a *telescope, we notice dark 
spots on its photosphere. By observing these spots, it is 
known that it turns on its axis in about 27 days ; also that 
its axis is inclined to the plane of the ecliptic [See Chap. 
IV.] Since we know that the Sun rotates on its axis, and 
its disk is always a perfect circle, we conclude, therefore,that 
the Sun is a perfect sphere. The Sun is 852,584 miles in 
diameter, and it is nearly 1,300,000 times larger than the 
earth. Its weight, however, is only about 300,000 times as 
great. 

The Sun is surrounded by a highly absorptive atmosphere 
which extends about 80,000 miles above its surface. In this 
atmosphere float incandescent clouds composed of vaporized 
metals and other constituent elements of a surface beneath. 
It is from these clouds whence the light so necessary to our 
existence is derived . 

The Sun is a variable star with a period of 1 1 years. 

We do not know what keeps up the Sun's great supply of 
light and heat, but we can theorize. A philosopher says, 
" One theory is good until a better one is given. " 

The constant supply of light and heat is supposed to be 
produced by the contraction of its cooling mass. 

Another theory is, that meteors are constantly falling into 

*Do not look at the Sun with even the smallest telescope, without proper instruc- 
tion and appliances, for it is very dangerous. Some astronomers have lost their eyes. 



18 ASTRONOMICAL GEOGRAPHY. 

the sun from interplanetary space. They arrive at its sur- 
face with enormous velocity, and being suddenly stopped 
their motion will be converted into heat. This theory, how- 
ever, is now generally discarded for the first . How long 
the Sun will continue to supply our system with light and 
heat is not known. Certainly it can not last forever if not 
replenished, and we have no evidence that such is the case. 
A body in giving out heat becomes cooler. Hence we 
conclude that the Sun at some time, cold and lonely, will go 
falling through infinite space. The ice will gradually creep 
from the poles to the equator on our own. terrestrial abode, 
and before its mighty tide man willdissappear from the face 
of the earth. Such we imagine will be the "end of the 
world . " Astronomers, however, have no evidence of any 
loss of heat for several hundred years. Should the sad 
spectacle above mentioned occur, it need not trouble us, for 
there is enough energy stored up in that radiant orb to sup- 
ply us with light and heat for many thousand years . The 
Sun is not stationary but is moving through space towards 
the constellation of Hercules at the rate of 4 miles per sec- 
ond. Many astronomers think our Solar System is revolv- 
ing around Alcyone, the brightest star of the Pleiades. 
Since the Sun carries with it ail of its attendants, we are 
constantly entering new realms of space. 

Before leaving the Sun let us again glance at its vast ex- 
tent in order to get it well impressed on our minds. 



ASTRONOMICAL GEOGRAPHY. 19 

If the Sun were a hollow shell and the Earth placed at its 
center, there would not only be enough room for the Moon 
to revolve at its actual distance (240,000 miles,) around the 
Earth, but each part of its orbit would still be nearly 200, 
000 miles below the surface of the Sun. A railroad train 
traveling at the ordinary rate, would perform its journey 
around the Sun in about 30 years. We feel humiliated be- 
fore its vast extent ; yet the Sun forms but a molecule of the 
luminous matter of the universe. 



LESSON IV. 



1. Planets. — A planet is a body that revolves around 
the Sun in an almost circular path. 

2. The Orbit of a planet is the path in which it travels. 

3. The planets are non-luminous bodies, and shine by 
reflecting the light of the Sun . 

4. The planes in which the orbits of the planets lie do 
not coincide ; but nearly so. 

5. The orbit of the Earth is called the Ecliptic. 

6. The plane in which the orbit of the Earth lies is called 
the Plane of the Ecliptic. 

7. Mercury. — Mercury is the nearest planet to the Sun 
whose existence is known. It may be seen in the West, 
just above the Sun, after that body has set, or after a certain 



20 ASTRONOMICAL GEOGRAPHY. 

time has elapsed, it may be seen in the morning before the 
Sun rises. Mercury is a little tinged with red and is the 
only planet that twinkles . Since its orbit is between us 
and the Sun it presents phases similar to the Moon. 
Its surface is rugged with mountains higher than those 
of the Earth. It has also evidences of a higher and 
denser atmosphere than our own. It revolves, around 
the Sun in a very eliptical orbit . When it is nearest the 
Sun it receives twice as much heat as when farthest away. 
It receives more than six times as much light and heat as 
our earth. Its mean distance from the Sun is about 
35,000,000 miles ; its diameter 2960 miles ; its day 24 hs., 
5 min., 30 sec. ; its year 88 of our days; the inclination on 
its axis, greater than that of the earth ; its seasons 22 days ; 
its volume }£ of the earth ; and its specific gravity about 7 ; 
that is, the average weight of its constituent parts is about 
7 times greater than the weight of an equal bulk of water. 
Owing to the great eccentricity of its orbit and the inclina- 
tion of its axis, its climate is subjected to great extremes. 
" Every 44 days on an average there is a change in temper- 
ature nearly equal to the difference between frozen quick- 
silver and melted lead-" 

8. Venus. — Venus is the second planet from the Sun . 
Owing to its comparative nearness, it appears the largest 
and brightest planet. It is surrounded by a transparent at- 
mosphere in which float the clouds that rise from its stormy 



ASTRONOMICAL GEOGRAPHY. Zl 

sea, presenting the same spetacle to us, we see every day 
on the Earth, 

It rotates on its axis in 23 hrs. 21 min. Its inclination to 
a perpendicular to the plane of its orbit is very great, (49 
58') and it is, therefore, like Mercury subjected to great 
extremes of temperature. 

It revolves around the Sun in 224^ of our days, which 
is the length of its year. Its mountains are higher than 
those of the Earth. 

Its mean distance from the Sun is about 66,000,000 miles, 
its diameter is 7,510 miles ; its specific gravity about five 
and one-fifth; its volume about four-fifths of the Earth. 
It receives twice as much light and heat as the Earth. 
Venus being between us and the Sun, it presents phases 
similar to Mercury. The phases of both planets, however, 
are not visible to the naked e\e. 

Venus may be seen in the evening in a certain part of the 
year. It is then known as the Evening Star. After an elapse 
of a few months it may be seen in the morning before the 
Sun rises. It is then known as the Morning Star. 

The planets we have already considered, are called in- 
ferior planets ; those which lie outside of the Earth's orbit 
are called superior planets. 

9. Mars — Passing the Earth to be dealt with hereafter, 
we come to Mars the fourth planet in order from the Sun . 
Its day is about the same length of ours ; its year about 687 



22 ASTRONOMICAL GEOGRAPHY. 

of our days; its diameter 4920 miles ; its inclination of 
its axis about the same as the Earth, and, hence, its seasons 
about the same. 

Mars has land, water, snow, clouds and mists the same 
as the Earth. You remember the color of the setting Sun 
is red. This is due to the absorption of its light in our at- 
mosphere. The color of Mars is of a fiery red. This 
is due to the absorption of a part of the Sun's light ; that is, 
the atmosphere of Mars acts as a sieve and stops all of the 
Sun's light but the red which it reflects to us. 

A large white spot surrounds the south pole of Mars, 
and is supposed to consist of ice and snow. The orbit of 
Mars is very eccentric and the south pole being inclined to- 
wards the Sun when it is in that part of its orbit nearest the 
Sun, we would naturally expect the white spot to decrease 
during the planet's summer in its southern hemisphere. Now 
this is exactly what happens . Hence, the supposition that 
the white spot is a snow zone is very plausible. The mean 
distance of Mars from the Sun is about 139,000,000 miles. 



LESSON V. 



1. Jupiter. — Omitting the Asteroids of which we shall 
soon have something to say, we arrive at Jupiter, the larg- 
est planet of our system, and the fifth in order from the Sun. 



ASTRONOMICAL GEOGRAPHY. 23 

It is 1,400 times larger than the Earth ; its mean distance 
from the Sun is about 476,000,000 miles ; the light and heat 
it receives from the Sun, but one-twenty-fifth as intense as 
that received by the Earth ; its day about 10 hrs., making it 
rotate so rapidly that a point on its equator travels about 27 
times faster tnan one on the Earth's equator. Owing to 
its very rapid rotation the flattening of its poles is very 
great, its equatorial diameter being one-sixteenth longer 
than its polar. The axis of Jupiter is only inclined 3 4' to 
a perpendicular to the plane of its orbit. Hence there is 
no perceptible change of seasons . 

Its year is equal to about 12 of our years. Jupiter is 
nearly as brilliant as Venus, and is always in the Zodiac 
[Lesson XIII] which makes it easily recognized. Its 
specific gravity is about 1^, which makes it weigh 300 
times as much as the Earth . 

2. Saturn. — Saturn, the sixth planet in order from the 
Sun, is 734 times as large as the Earth. It rotates very 
rapidly on its axis ; its days being only 10% hours long. 
Its year is equal to about 29^ of our years ; the inclination 
of its equator to the plane of its orbit 26^°, and, hence its 
seasons are subjected to changes similar to those of the 
Earth ; its mean distance from the Sun is about 872,000,000 
miles ; and its specific gravity only two-thirds. 

Around Saturn, 20,000 miles above its equator, rises a 
huge flat ring. This ring is followed by a second and the 



H 



ASTRONOMICAL GEOGRAPHY. 



second by a third. This system of multiple ring's is only 
about ioo miles thick but it is 160,000 miles in diameter and 
38,000 miles broad. 

The ring's are not stationary, but revolve around Satura 
with greater rapidity than the planet itself. Close observa- 
tion has revealed that the rings are undergoing changes. 




Fig. 4.— Saturn and its rings compared as to size with the Earth. 

The general supposition is that these rings are composed 
of many little satellites, each moving independently in its 
own course around the planet, and being closely packed to- 
gether, they present the appearance of bright rings. 

3. Uranus. — The six planets already named were known 



ASTRONOMICAL GEOGRAPHY, 25 

to the ancients . The rest have been discovered in modern 
times . 

In 1 78 1, Sir William Herschel discovered the seventh 
planet in order from the Sun, and it is called Uranus . It is 
just visible to the naked eye. Its year is equal to 84 of 
our years, but there being no spots on its surface, we are not 
able to tell its period of rotation. It is 72 times as large as 
the Earth ; its specific gravity is nearly 1. The mean dis- 
tance from the Sun is 1,754,000,000 miles. 

4. Neptunk — The discovery of Neptune is one of 
the grandest triumphs of modern science. 

Every molecule of matter in the universe attracts every 
other molecule, and after taking all the known causes into 
account, there was still something that effected the motions 
of Uranus . This led to the belief that there was another 
planet beyond the orbit of this planet. Le Verrier, a French 
astronomer, proved by a mathematical calculation that there 
must be another planet beyond the orbit of Uranus, and 
wrote to Berlin observers, telling them where he imagined 
the planet to be . Following Le Verrier's directions, the 
planet was discovered the same evening. (September 1846.) 

Like Uranus, Neptune's period of rotation is un- 
known ; its year is equal to 165 of our years ; its specific 
gravity nine-tenths, and its mean distance from the Sun is 
2,746,000,000 miles. 



26 ASTRONOMICAL GEOGRAPHY. 

The intensity of its light and heat is only about one-nine 
hundredth as great as that of the earth. 

5. The Planets in General. — The eight planets al- 
ready named in the order of their sizes are : Jupiter, Saturn, 
Neptune, Uranus, Earth, Venus, Mars and Mercury. On 
account of their large size they are called Major Planets, 
the remainder are very small and are called Minor Planets, 
or Planetoids. 



LESSON VI. 



1. The Asteroids — The Asteroids,or minor planets re- 
volve around the Sun between the orbits of Mars and 
Jupiter. Their average distance from the Sun is about 
260,000,000 miles. The discovery of the asteroids is due 
to what is known as Bode's Law. Let us write down 
o 3 6 12 24 48 96 

and add 4 to each number ; we now have 
4 7 10 16 28 52 100. 

This series of numbers represents the distances of the 
ancient planets from the Sun . 4, represents Mercury ; 7, 

Venus ; 10, Earth ; 16, Mars ; 28, ; 52, Jupiter ; 

an 100, Saturn. 28 has apparently no planet to represent. 
Kepler boldly placed an undiscovered planet in the gap, 
but up to the discovery of Uranus the suspected planet had 



ASTRONOMICAL GEOGRAPHY. 27 

not revealed itself. When, however, this planet was dis- 
covered, and it was found that the next number in . Bode's 
series, 196, would represent its distance, a society of astron- 
omers was formed, and search made for it. 

On Jan. 1, 180G, Ceres was discovered which filled up 
the gap. Since that time many others have been added, 
and there are now (1887) 264, known to exist 

Only two of these planets, Ceres and Vesta, are some- 
times visible to the naked eye ; the largest being only 228 
miles in diameter. The force of gravity must be very 
small. The inhabitants of these planets can all be clowns, 
for a man could easily jump 50 feet high on one of their sur- 
faces and sustain but a slight shock on descending. There 
are evidences of an atmosphere on some of the planets. 

Some of them also seeem to rotate on their axis. 

It is generally believed that the minor planets are the frag- 
ments of a large planet shattered by coming in contact with 
some other heavenly body. 

According to Le Verrier's computation there must be 
about 150,000 ! of these little bodies between the orbits of 
Mars and Jupiter . 

2. Satellites — Those planets which revolve around the 
Sun as a center, are called primary planets. Those which 
revolve around the primary planets, are called secondary 
planets or satellites. Since the secondary planets accom- 
pany the primaries around the ^un, and the Sun moves 



28 ASTRONOMICAL GEOGRAPHY. 

through space, we see that the motions of the satellites is 
a very complex subject. 

The Earth has -one satellite called the Moon ; Mars two ; 
Jupiter four ; Saturn eight ; Uranus six ; Neptune one. 

The satellites, with the exception of those of Uranus and 
Neptune, revolve around their primaries the same direction 
that these planets rotate, namely? from West to East. 

The primaries all revolve around the Sun from West to 
East, or in the opposite direction to the hands of a clock. 
There being such a wonderful uniformity in the direction of 
rotation and revolution of the planets and their satellites so 
nearly in the same plane, it has led to a very popular and 
plausible hypothesis now used almost exclusively by scien- 
tists tc explain how the Solar System originated. 

3. Laplace's Nebular Hypothesis — This hypothesis 
was advanced by the celebrated French astronomer, Laplace. 
It assumes that all the matter now belonging to the Solar 
System was once scattered throughout the space now oc- 
cupied by that system, in a highly heated condition, forming 
a vast Nebula which probably extended far beyond the or- 
bit of Neptune . 

By and by the mass began to cool and the force of gravity 
overcame the repellent force of heat, and the matter con- 
stituting it began to contract. 

It is a very well known law in Philosophy that whenever 

t 



ASTRONOMICAL GE0GRAPH1. 29 

matter seeks *a center a rotary motion is acquired. 

As the cooling mass contracted the rotary motion neces- 
sarily increased ; the centrifugal force at the surface over- 
came the force of gravity and ring like masses of nebulous 
matter were thrown off and collecting in spherical masses, 
they formed the planets which for a similar reason acquired 
a rotary motion and detached their satellites* 

If this supposition is true, when the rings of Saturn were 
thrown off several of them did not break up into globes but 
still remain as rings revolving around the planet. It is very 
probable that if these rings have not already broken up into 
many little satellites, that they will sometime do so, Mitchell 
very appropriately remarks that " Saturn's rings were 
left to show us how the world was made. " The ring which 
formed the Asteroids probably broke up into many frag- 
ments, ncne large enough to attract the rest, and form a sin- 
gle globe ; while the central mass of the nebula contracted 
and formed the Sun. 

The theory is perfectly consistent with strict mechanical 
principles, yet we must remember that it is only a hypoth- 
esis, and it must be dealt with as such 

We should also remember that the strongest evidence to 
confirm the truth of any theory is its ability to explain 
phenomena, and this is strikingly true of this hypothesis. All 
observations tend to prove its correctness. The theory bt 

-Examples of this law are seen in every day life, as water poured into a funnel, 
a whirlwind or a water-spout. 



30 ASTRONOMICAL GEOGRAPHY. 

ing sustained by so mar^ facts, we shall entertain it in the 
absence of positive counter evidence. 



LESSON VII. 



i. The Moon. — The Moon is 2,153 miles in diameter. 
It would take 49 Moons to make a planet as large as the 
Earth. 

Its orbit is very eliptical, the center of the earth being at 
one of the foci ; its average distance from the Earth is 
nearly 240,000 miles. When in that part of its orbit nearest 
the earth, it is said to be in perigee, and when in that part 
of its orbit farthest awa)' it is said to be in opogee. To an 
inhabitant of the Moon the Earth must look at least twelve 
times as large as the Moon looks to us; while the Earth's 
phases would be similar to those we see in the Moon. The 
eclipse of the Earth would be on a much smaller scale than 
the eclipse of the Moon and the eclipse of the Sun would 
be a phenomenon many times greater than we see on the 
earth. It makes one revolution from West to East around 
the Earth in 27^ days. This period is called the sidereal 
month. The Earth in the mean time traveling around the 
Sun changes its position with respect to the Sun, so that it 
takes the Moon about 29^ days to make one revolution 
with respect to the Sun. This is called the synodic 
month, and is the time from one New Moon till the next. 



ASTRONOMICAL GEOGRAPHY, 31 

The Moon rotates on its axis from West to East in ex- 
actly the same time in which it accomplishes its sidereal 
revolution, hence we never see but one side of our satellite. 
Viewed with a most powerful telescope the Moon appears 
as it would to the naked eye 80 miles away. 

It has no atmosphere, hence to an observer on the Moon 
it would present a very peculiar aspect. There is no sound ; 
no wind ; no cloud to dot the sky. There being no atmos- 
phere to reflect the Sun's rays, there is no twilight in the 
morning or evening, but the light of day comes like a flash, 
and goes as quick as it came. 

There a person can not see through his own shadow, but 
every place where the direct rays of the Sun do not reach 
is a? a deep, dark dungeon, through which we can not see . 
No water is there to quench one's thirst ; but everything is 
a rainless desert as quiet and voiceless as the grave. 

2. The Moon's Phases — The Moon is a non-luminous 
body and like the planets, it shines by reflecting the light of 
the Sun. 

When the Moon is between the Earth and the Sun, the 
side turned away from the Earth is lit up, because it is turn- 
ed toward the Sun ; while that part turned toward us is in- 
visible, because it is turned away from the Sun . We then 
have New Moon. 

As the Moon progresses in the course of its revolution, 
it gradually presents its illuminated portion to us, and we get 



SB 



ASTRONOMICAL GEOGRAPHY- 



a glimpse, as it were, of the bright side for a little while after 
sunset. We then have the Crescent Moon. 

When the two lines passing from the Moon to the Earth 
and Sun, respectively, form a right angle, we see one half of 
the illuminated side. We then have the First Quarter. 




Fig. 5.— The Moon's Phases. 

Next we see more than one-half of the Moon's disk. We 
then have Gibbous Moon. 

Again we have the Earth between the Sun and Moon, and 
we see all of the illuminated portion. We then have Full 
Moon. 

From Full Moon we have similar phases in reverse order 



ASTRONOMICAL GEOGRAPHY. 33 

until New Moon is again reached, when the cycle recom- 
mences. 

From New Moon to Full Moon our satellite is said to wax 
or increase, while from Full Moon to the next New Moon, 
it is said to wane or decrease. 

3. Eclipses. — If the orbit of the Moon coincided with the 
plane of the ecliptic, every time we have a New Moon 
that body would pass directly between us and the Sun, and 
shut off the Sun's light. This, however, is not the case. 
The plane in which the Moon performs its journey around the 
Earth, is inclined five degrees to the plane of the ecliptic. 
Hence we see that one half of the Moon's journey is per- 
formed North of the plane of the ecliptic and the other 
half South of it. 

The orbit of the Moon must, therefoie, pass through the 
plane of the ecliptic at two points. These points are called 
Nodes. Now if the Moon happens at either of these 
nodes, when they are in line with the Earth and Sun, we 
have an eclipse. If the Sun and Moon are in conjunction, 
the New Moon passes between the Earth and Sun we 
have an eclipse of the Sun, the Earth passing through the 
shadow of the Moon ; but if the Sun and Moon are in op- 
position, the Full Moon enters and is hidden in the shadow 
of the Earth, and we have an eclipse of the Moon. 

Since the Earth casts a larger shadow than the Moon, an 
eclipse of Moon lasts longer than one of the Sun. 

If the Moon is near but not exactly at a node we have a 
partial eclipse. 



34 ASTRONOMICAL GEOGRAPHY. 

Effects of Eclipses Upon the Ignorant. — We have 
neither time nor space to describe the effects of eclipses 
upon the ignorant masses. One illustration will suffice. 
Early in the year of 1504, Christopher Columbus, and crew, 
while on a voyage of discovery, were wrecked on the coast 
of Jamaica. They were on the point of starvation, and the 
natives refused to give them any provisions. Columbus 
knew that an eclipse of the Moon would occur on the night 
of March 1, of that year. Resorting to a stratagem, he 
told the natives that the Great Spirit was angry with them 
because they did not treat the Spaniards better, and would 
hide his face from them that night. The eclipse came and 
provisions came also, for when the Moon became dark, the 
Indians believing that Columbus had told the truth brought 
him bountiful supplies, beseeching him to induce the Great 
Spirit to receive them again into his favor. 

Such superstition as this has stained the horizon of a 
thousand years with innocent blood, but a new era is now 
being ushered in, full of science and progress. 



LESSON VIII. 



Comets — We have other bodies revolving around the Sun 
besides the planets. They are masses of self luminous gas 
and are called Comets. They travel around the Sun in very 



ASTRONOMICAL GEOGRAPHY. 85 

elongated orbits ; some of them completeing the cycle in a 
few years, while others require many thousand years. In- 
stead of all revolving around the Sun from west to east like 
the planets, some of thern revolve from east to west, while 
others strike the plane of the ecliptic at various angles. 

Did you every see a comet ? It is a glorious spectacle 
projected on the sky. Its brightest portion is called the 
Coma or head. Some times the head contains a bright spot 
called the Nucleus. 

The dimmer portion flowing from the head is called the 
Tail. All parts of the comet are of a very transparent na- 
ture. Stars may be seen through the tails where they are 
thousands of miles in diameter. Comets travel very slow 
when far away from the Sun, but their rate of travel greatly 
increases asthey approach that body. Their brightness also 
increases as they approach that luminary. Gets of gas 
burst violently forth from the head towards the Sun, and 
being driven back, probably by the repulsive power of the 
Sun, a tail is formed varying from a million miles to more than 
one hundred million miles in length. The tail always points 
away from the Sun no matter whether the comet is travel- 
ing to or from the Sun . 

2 . Effects of Comets Upon the Ignorant. — Com- 
ets are usually regarded by foolish people as the sign of 
war, pestilence, and famine. Many people believe that the 
great comet of 1861 foretold the War of Secession. 



36 



ASTRONOMICAL GEOGRAPHY. 



It has long been feared that our Earth would sometime 
have a collision with some of these wanderers, and that they 
would destroy it ; but the light of Modern science informs 
us that the mass of a comet is so extremely light and rare 
that we need not apprehend any danger. 

In fact we have good evidence that our Earth passed 
through the tail of the brilliant comet of 1861, yet the only 
unusual phenomenon was a peculiar phosphorescent mist. 

In 1776 a comet became entangled with the satellites of 
Jupiter, but the satellites pursued their journey around their 
primary as though nothing had happened, while the comet 
was thrown entirely out of its course and instead of being 
a long-period comet, it now accomplishes its revolution in 
about 20 years . 

The following table will prove useful as a reference : 



Comets. 



En eke' s . 
De Vico's. 
Brorsen's.. 
Biela's ... 
Faye's . . . 
flalley's 



Time of Revolu- Nearest approach Greatest distance 
tion. to the Sun. from the Sun. 



YEAKS. 


MILES. 


MILES. 


3M 


32.000,000 


387,000,000 


6|| 


110,000,000 


475,0C0,000 


64,000,000 


537,000.000 


82,000,000 


585,000,000 


1X 4 


192,000.000 


603,000,000 


56,000,000 


3,200,000,000 



3. Meteors — Go out on a clear night and the chances 
are you will see what you fancy to be stars shooting across 
the sky. These are small bodies called meteors which 
revolve around the Sun like planets, and are composed of 
metallic iron and various compounds of silica. The 



ASTRONOMICAL GEOGRAPHY. 37 

greatest fall of meteors is about the 14th of November. 

It has been calculated that these bodies revolve around the 
Sun in an eliptical orbit whose perhehon lies in the Earth's 
orbit and its aphelion just beyond the orbit of Uranus ; that 
its inclination to the plane of the ecliptic is 17 . And that 
the motion of these bodies is from east to west is proven be- 
yond doubt. The Earth sailing along in its orbit en- 
counters the meteors at their perihelion point about Nov . 
14th. Hence the Nov. shower. They do not seem to be 
uniformly distributed throughout their orbit, but travel in 
several groups. Up to this time 56 such collections have 
been detected. These groups complete their revolution in 
about 33 years, and hence those great November showers, 
which make the sky put on a phosphorescent appearance, 
only occur at intervals of 33 years ; but as they extend a 
great distance along their orbit, they are several years in 
passing one point. We may, therefore, expect brilliant 
showers for two or three consecutive years. The last great 
shower was in 1866, while the same phenomenon will again 
occur in Nov. 1899 or I 9°°* 

Traveling at the rate of 30 miles per second, they enter 
our atmosphere which acting as a break makes them so hot 
by its friction that they are usually vaporized before reach- 
ing the solid earth, and leave a train of luminous matter be- 
hind them. Many, however, reach the earth, often greatly 
damaging whatever happens in their way. Some of the 



88 ASTRONOMICAL GEOGRAPHY. 

larger ones even explode on becoming intensely heated ; the 
fragments consisting of red hot stones being scattered over 
an area of several square miles 

Meteors bear evidences of having been in such a highly 
heated condition as to be in a state of fusion . How these 
little bodies were "created" has never been satisfactorily 
explained. 

4. The Zodiacal Light — The Zodiacal Light may be 
seen at certain times in the west just after sunset and in the 
east before sunrise. Its shape is that of a cone ; its base is 
turned toward the Sun ; and its axis lies in the plane of the 
ecliptic. Its true position in the Solar System is only a mat- 
ter of conjecture. Some think it is due to a great multitude 
of meteors which surround the Sun and reflect its light ; 
others attributed to an immense number of these little bodies 
which are constantly entering and being burnt up in our own 
atmosphere. 

What the Zodiacal Light is, is, therefore, only an opinion 
based upon an imperfect knowledge. 



SECTION II. 



LESSON IX. 

i. The Earth.— In discussing the planets we passed 
over the Earth. We shall now have a great deal to say 
about it. The Earth is the planet upon which we live 
and like other planets it revolves around the Sun ; its orbit 
lies between the orbits of Mars and Venus ; its mean dis- 
tance from the Sun is about 91,500,000. 

, It was formerly supposed that the Earth was stationary 
and that it rested on something,probably, the back of an ele- 
phant . The elephant was supposed to stand on the back of 
a turtle. What the turtle stood on remains unanswered. 
("Probably there are turtles the rest of the way down.") 

Nothing is more false than such a theory. The earth 
rests on nothing. Being isolated from the other heavenly 
bodies, it moves through empty space around the Sun. 

Before studying the motions of the eartn we must needs 
first study the relations between matter and force, concisely 
expressed in several laws discovered by Sir Isaac Newton. 

2. Law of Inertia. — A body at rest remains at rest, 
and a body in motion moves with uniform velocity in a 



£0 ASTRONOMICAL GEOGRAPHY. 

straight line, unless acted upon by some external force to 
change its condition. 

Lay a book or other inanimate object upon the table and 
it will remain there until somebody or some external force 
moves it, because it has no power within itself to change its 
position . 

Hurl a stone into the air. If acted upon by no external 
force, it will move onward forever, because it has no more 
power to stop than it had to start. Hence we see that mat- 
ter has the property of keeping in motion when in motion, 
and remaining at rest when at rest. This property is called 
Inertia. The Law of Inertia is known in Physics as New- 
ton's First Law of Motion. 

3. Law of Universal Gravitation — When you threw, 
the stone into the air it fell to the earth . What external 
force was the cause of its falling ? We have told you in a 
previous lesson that every molecule of matter in the universe 
attracted every other molecule. The mutal attraction be- 
tween particles of matter is called gravitation. 

Now when you threw the stone skywards, its motion was 
lost on account of the resistance of the air and the attrac- 
tion of the Earth. 

The force of gravity of a sphere or spheroid acts upon a 
body of matter without it as if the attractive force was con- 
centrated at its center, and this attraction varies inversely as 
the square of its distance from the center. 



ASTRONOMICAL GEOGRAPHY. 



41 



For example, take a man that weighs 1 80 lbs. at the 
Earth's surface. What would he weigh if transported 8,000 
miles above its surface ? 

Suppose the surface of the Earth to be 4,000 miles from 
its center . Then the man would be 4,000 plus 8,000 which 
is 12,000 miles from the Earth's center, or 12,000 divided by 
4,000 equals 3 times as far as when he weighed i8olbs. 

The square of 3 is 9. Hence he would weigh one-ninth 
of 180 or 20 lbs. 

What would he weigh at the Earth's center ? 

Nothing because he would be equally attracted on all 
sides . 

If the force of gravity would cease what would be- 
come of the rocks, houses and the living beings that it holds 
to the earth ? 




Fig. 6. 



4. Newton's Second Law of Motion. — A given 
force has the same effect in producing motion, whether the 



42 ASTRONOMICAL GEOGRAPHY. 

body on which it acts is in motion or at rest ; whether it is 
acted upon by that force alone, or by others at the same 
time. 

In Fig. 6 suppose a ball at A to receive an impulse that 
sends it to B in one second ; then suppose it to receive 
another impulse at right angles to the line A B, that sends it 
to C in one second . Now instead of these forces acting sep- 
arately, let us suppose that they both act at the same time, 
and that they be applied at A, at right angles to each other. 
The ball will then move over the diagonal A C of the par- 
allelogram A B C D, and at the end of one second it will be 
found at C. Hence the Second Law of Motion. 



LESSON X, 



i . The Earth has two motions . It rotates on its axis 
and revolves around the Sun . The former is called its 
diurnal or daily motion ; the second its annual or yearly 
motion. 

2. Cause of the Earth's Revolution — When the 
Earth was separated from the Nebulous Sun, it received a 
projectile force which has ever since been the cause of its 
motion through space. From its inertia alone, it must con- 
tinue moving forever. 

This motion, however, would be in a straight line if it 
were not for the gravitation of the other heavenly bodies . 



ASTRONOMICAL GEOGRAPHY. 



43 



This attraction causes, as we shall now explain, the curved 
paths of the planets. 




Fig. 7. 



In fig. 7, S represents the Sun ; E the Earth. From its 
inertia, the Earth would move for an indefinite time in the 
direction E F, but the Sun's attraction constantly act- 
ing upon the Earth at right angles to its orbit causes our 
planet to change its direction at every point, by falling to- 
ward the Sun, and instead of traveling along the line E F 
or E S, its true path is between these lines along the curve 
lineE B. 

The inertia is sometimes called the centrifugal force, while 
the Sun's attraction is called the centripetal force. It is 
these two forces acting together that insures the safety of our 
world. If the centripetal force would cease at B, the 
Earth would pass off into space along the straight line B M, 



44 ASTRONOMICAL GEOGRAPHY. 

but if the inertia would cease at B, the Earth would fall to 
the Sun along the line B S, and arriving at that luminary in 
64 days after it started, it would disappear in its surface like 
a meteor in our own atmosphere. 

3. Proofs that the Earth Revolves. — There are 
many proofs of the Earth's revolution. Only a few of the 
more simple can be fully explained in a work like this. 

1st. The change of seasons [Lesson XIX J is a proof 
of the Earth's revolution. 

2d. All the stars in the firmament make one mere ap- 
parent revolution in one year around the Earth than the Sun. 
This can only be satisfactorily explained on the supposition that 
the Earth revolves around the Sun. 

3d. Kepler's First Law. — Each planet describes 
around the Sun an eliptical orbit, and the center of the Sun 
occupies one of the foci. 

4th. Kepler's Third Law. — The Earth is also included 
under Kepler's Third Law which is as follows : If the 
square of the time of revolution be divided by the cube of 
its mean distance from the Sun, the quotient will be the 
same for all the planets . 



LESSON XL 

1 . Cause of the Earth's Rotation — When the Earth 
began its existence, after it had been separated from the 



ASTRONOMICAL GEOGRAPHY. 45 

Nebulous Sun,its matter began to accumulate around a cen- 
ter on account of the contraction of its cooling mass. Hence 
it acquired a rotary motion. According to Lockyer the time 
of rotation has not changed, if any, more than one-sixty 
sixth of a second in 2,500 years, 

2. Proofs that the Earth Rotates — 

1st, From the laws of centrifugal force, it is impossible 
for the Sun and stars to revolve around the Earth. Hence 
the only natural conclusion is that the Earth turns on its 
axis. 

2d. If the Earth rotates on its axis, its surface midway 
between the poles, known as the Equator, must necessarily 
travel fastest, while the motion decreases until it reaches the 
poles where ii is zero. Hence from the greater centrifugal 
force, a body ought to loose some weight in being transport- 
ed from the poles to the equator . This is exactly what 
happens. A body looses one two hundred and eighty-nineths of 
its weight upon being taken from either pole to the equator. 
From a law in philosophy, that the force increases as the 
square of the velocity, and since 2891s the square of 17, if 
the Earth turned 17 times faster, a body at the equator 
would wiegh nothing, while a stone hurled into the air would 
never fall to the earth. 

3d. Drop a plumb-line from the top of a high tower to 
the earth and mark where it touches the ground ; then let a 
stone fall from the same point of the tower. It falls to the 



46 ASTRONOMICAL GEOGRAPHY. 

east of the point marked. This shows that the Earth ro- 
tates from west to east. 

4th. Foucault proved, by a pendulum experiment, that 
the earth rotates. 

5th. The oblateness of the earth is the legitimate result 
of its diurnal motion. 

3. Shape of the Earth. — The true shape of the 
earth is that of an Oblate Spheroid. The equatorial 
diameter is twenty-six and five elevenths miles longer than 
the polar. 

4. Proofs that the Earth is Round. — The earth be- 
ing such a large sphere its surface everywhere appears flat. 
We shall, however, give ten proofs that it is spherical. 

1st. Circumnavigation. — You all know that a fly can 
walk around an apple, so, too, a person can travel around the 
earth. Ships have often started at a certain place on the 
earth's surface, and by continuing in one direction for many 
weeks, have reached the starting point. This would be im- 
possible, if the earth is not spherical. 

2d. The Sensible Horizon. — A person on top of a high 
mountain can see the earth slope away in all directions. The 
higher a person ascends, the more the circle formed by the 
apparent meeting of the earth and sky, is extended . 

3. Approaching Objects. If the earth was flat a per- 
son could see the lower half of an object as soon as the 
upper half. This, however, is not the case. When a ship 



ASTRONOMICAL GEOGRAPHY. 47 

is coming into port, we first see the topmast, next the sails, 
and lastly, the hull meets our view. 

Since this phenomenon occurs no matter from which di- 
rection the ship is approaching us, we conclude, therefore, 
that the earth is spherical. 

4th. Shape of the Horizon — The line where the earth 
and sky seem to meet is always the circumference of a cir- 
cle. Now, if the Earth were flat, this would not be true, 
since to a person near the edge some other shape would 
meet our view. 

5th. The Earth's Shadow — During an eclipse of the 
Moon, the Earth always casts a circular shadow upon our 
satellite. Since only spherical bodies cast circular shadows 
in all directions, the Earth must be spherical. 

6th. Walls of a Building. — The opposite walls of a 
building, if built perpendicular are farther apart at the top 
than at the bottom. 

7th. Rising and Setting of the Sun. — If the earth 
were flat the Sun would rise and set everywhere at the 
same time. We know, however, that the Sun rises and 
sets east of us before it does west of us. 

8th. Position of the North Star. — The North Star 
never sets. This would be impossible, if the earth was not 
spherical. 

9th. Unequal Length of Day and Night. — If the 
Earth were flat, day and night would everywhere be of 



AS ASTRONOMICAL GEOGRAPHY. 

equal length, throughout the year, Since this is not the 
case, we again infer that the Earth is spherical, 

ioth. Measurement — By actual measurement we not 
only find that the Earth is an oblate spheroid, but also the 
exact amount of its oblateness. 



LESSON XII. 

i. Dimensions and Density of the Earth — The polar 
diameter of the Earth is 7,899 and one hundred and ninety- 
nine five hundred and twenty-eighths miles, while the equa- 
torial diameter is 7,925 and four hundred and thirty-eight 
five hundred and twenty-eighths miles. The circumferance 
is about 24,899miles, while the area of its surface is nearly 
197,000,000 square miles. Of this only about 53,000,000 
square miles is land area, while the remaining 144,000,000 
square miles is water area. 

The specific gravity of the Earth is about 5^3, and its 
weight in round numbers is 6,000,000,000,000,000,000,000 
tons ! 

2. Cause of the Earth's Oblateness — The oblate- 
ness of the earth is due to its rotation which caused it to 
bulge out at the equator, and put on its present shape, when 
it was in a fluid condition. 

3. Does the Mississippi River Run up Hill ? — Since 
a river that flows towards the Equator has its mouth farther 



ASTRONOMICAL GEOGRAPHY. 49 

from the center of the Earth than its source, it ma}', there- 
fore, be truly said that it flows up hill, because up only means 
away from the center of the Earth, while down means to- 
wards the center of the Earth. For simplicity let us im- 
agine a person at the Earth's center. He would look up no mat- 
ter in what direction he would turn his head. 

Again let us imagine a person at the equator and another 
at the poles to be looking down upon the person at the cen- 
ter. These persons would not look in the same direction, 
but on the contrary, they would look at right angles to each 
other. 

Since up is away from the earth's center, and the mouth 
of the Mississippi river is over four miles farther from this 
center, than its source, it must, therefore, flow up hill . 

4. Why Some Rivers Run up Hill. — The same 
force which caused the earth to bulge out at the equator, 
also causes those rivers which flow up hill to do so. If the 
earth would cease to rotate, the waters of the Mississippi as 
well as those of the sea would all rush towards the poles, 
leaving the bottom of the sea dry at the equator, while the 
polar regions would be one vast sea, whose surface would 
everywhere be an equal distance from the earth's center. 

5. POINTS 

1st. Horizon. — The place where the earth and sky 
seem to meet is called the Sensible Horizon. 



50 ASTRONOMICAL GEOGRAPHY. 

2d. Zenith. — The Zenith is a point in the heavens di- 
rectly overhead. 

3d. Nadir. — The Nadir is a point directly underfoot. 

dth. North. — North is the direction , of the North 
Star. 

5th. South. — South is the opposite direction. 

6. East. — East is toward the place where the Sun 
rises. 

7th. West — West is toward the place where the Sun 
sets. 

8th. Equinoctial Points — Equinoctial Points are the 
points where the Sun crosses the Equator. 

9th. North, East, South and West are called the Cardi- 
nal Points . 

10th. The points midway between the cardinal points 
are called Semi-Cardinal Points. 



LESSON XIII. 



1. Imaginary Lines — For the purpose of locating places 
upon the Earth, we imagine it to be encircled by curve lines, 
the circumf er ences of circles. 

(a) A Great Circle divides the earth into two equal 
parts. 

The shortest distance between any two points on the 
earth's surface is along the arc of a great circle. 



ASTRONOMICAL GEOGRAPHY. 51 

\b) A Small Circle is one that divides the earth into 
two unequal parts. The lines most frequently used in 
geography are the Equator, the Meridians, and the Par- 
allels . 

(c) The Equator is the circumference of that great 
circle which is equidistant from the poles, and which divides 
the earth into a northern and southern hemisphere . 

(d) The Tropics are parallels which lie about 23.5! de- 
grees (exactly, 23 , 27', 24",) north and south of the 
equator. The one north of the equator is called the Tropic 
of Cancer, while the one south of it is called the Tropic of 
Capricorn , 

The tropics are situated where they are because the Sun's 
vertical rays always stay within them. 

(e) The Polar Circles are parallels which lie 23*4 de- 
grees from the poles. The one in the northern hemisphere 
is called the Arctic Circle, while the one in the southern 
hemisphere is called the Antarctic Circle* 

(f) Meridians are the semi-circumferences of great cir- 
cles, which are drawn from pole to pole. Of course there 
is an infinite number of meridians and parallels, since there 
is one of each passing through every point on the earth's 
surface. 

2. Latitude.— Latitude is distance north or south of the 
equator expressed in ° ' ". It is measured on the merid- 
ians by the parallels. 



52 ASTRONOMICAL GEOGRAPHY. 

Since the poles have the greatest distance possible from 
the equator of any object on the earth's surface, and that 
distance is ^ of the circumference of a circle, the greatest 
latitude a place can have is % of 360° or 90 . The equator 
has no latitude. Places north of the equator are in North 
Latitude, while those south of that line are in South Lat- 
itude. 

3. Longitude.- — Longitude is the distance east or west 
of some established meridian expressed in ° ' ". It is 
measured on the parallels by the meridians, with the excep- 
tion of those places situated upon the equator, whose longi- 
tude is measured upon the equator by the meridians. 

The meridian from which time is reckoned is called the 
Prime Meridian . Nations usually reckon from the meridian 
of their own capitols. For example, the English reckon 
from the meridian which runs through the observatory at 
Greenwich, while we Americans reckon from Washington. 
A place east of the prime meridian is in East -Longitude ; 
a place west of this meridian is in West Longitude. 

Since there are only 180 in a semi-circumference, the 
greatest longitude a place can have is 180 , for if a place 
be situated more than 180 in east longitude, it will fall in 
less than 180 west longitude. 

The prime meridian and the poles have no longitude. 

The place where the prime meridian crosses the Equator 
has neither latitude nor longitude. 



ASTRONOMICAL GEOGRAPHY. 53 

4. Value of Degrees of Latitude — Since latitude is 
measured on the meridians, the value of a degree of latitude 
is one three hundred and sixieth of the circumference of a 
great circle. On account of the Earth's flattening at the poles, 
the Earth's surface does not curve as fast as we approach 
those points as it does at the equator, and hence the merid- 
ians in high latitudes represent the circumferences of larger 
circles than they do at or near the Equator . 

One degree of latitude is, therefore, longer at the poles 
than it is at the equator . The following table will prove 
useful as a reference. 



Place. 


LENGTH OF A DEGREE IN MILES. 


Equator. 
20 degrees . . 




68.69$ 

68.781 


40 " 


68.884 


60 " 

80 ** 


69.222 
69,375 
69.396 


m " ; 







5. Value of Degrees of Longitude — The value of a 
degree of Longitude is subjected to great variations. On 
the Equator it is one three hundred and sixtieth of the Earth's 
circumference, while at any other place it is one three hun- 
dred and sixtieth of the parallel passing through that place. 
The parallels, as we have seen, decrease in length as we ap- 
proach the poles, and, hence, the value of a degree of longi- 
tude must also decrease as the latitude increases, until the 
poles are reached, at which place, the value is zero* 



5A ASTRONOMICAL GEOGRAPHY- 

Consult the following table . 



Place. 


LENTH OF A DEGREE IN MILES. 


Equator 

15 degrees 


69.16 
66.82 
59.95 
48.98 
34.67 
17.96 
Zero 




30 " 




45 
65 






75 
90 







The above figures are given in common miles. A Geo- 
graphical or Nautical mile is one three hundred and sixtieth of 
a degree on the equator or about 2025 yards. It is used 
for measuring distances at sea. 

How long is the 45th parallel ? 

How can we find the distance around the earth on any 
parallel,when the length of one degree is known ? 



LESSON XIV, 



1 . Longitude and Time — For our present purpose it is 
true enough to say that the time from one Noon till the next 
is 24hrs. Since the Sun appears to travel around the Earth 
in 24hrs., in ihr., it will travel over one twenty-fourth of 
360 or 1 5 of longitude ; while in one minute of time it will 
pass over one sixtieth of 15 or 15' of longitude ; and in 
one second of time it will travel over one sixtieth of 15' or 
15" of longitude. 

Since the value of so many units of time is always equal 
to so many units of longitude, or vice versa a certain num- 



ASTRONOMICAL GEOGRAPHY. 55 

ber of units of longitude is always equal to so many units 
of time, it is evident that if the value in either is known,the 
value in the other may be found. 

2. The International Date Line or Sunday Line is 
the place where the days and nights are assumed to begin and 
end. It passes through the Pacific ocean . Immediately 
east of this line it is always one day earlier in the week 
than immediately west of it. For example, when it is 
Monday east of this line it is Tuesday west of it. ■ If we 
travel around the earth from east to west we loose a day, 
but if we travel around the earth from west to east we gain 
a day. Hence we see the necessity of a correction at this 
line or we would soon have a remarkable confusion of dates. 
Navigators, however, are in the habit of making this cor- 
rection at the 180th meridian from Greenwich. 

3. Time Varies — When the Sun's vertical rays fall per- 
pendicular upon any meridian, it is Noon (M, meridian) on 
that meridian ; east of this meridian the Sun's vertical rays 
have already passed, hence, it is afternoon (P M, postme- 
ridian) at such places. The Sun's vertical rays, however, 
have not yet reached those places situated west of this me- 
ridian, and, hence, it is forenoon (AM, antemeridian) at such 
places . 

4. Problem — Honolulu,Sandwich Islands, is in longitude 
I 57°5 5 2 ' west of Greenwich. Sidney, Australia, is in 15 1° 
1 1' east longitude. When it is five minutes after four o'clock 



56 ASTRONOMICAL GEOGRAPHY. 

on Sunday morning at Honolulu, what is the hr. and day of 
the week at Sidney ? 

5. Solution — Going westward from Honolulu to the 
180th meridian, we find that we have passed over the differ- 
ence between 180 and 157 , 52', which is 22 8'. Divid- 
ing this by 15 we have ihr., 28 min., 32sec. ot time. 

Since it is earlier at the 180th meridian by exactly this 
time, it must be 2 o'clock, 36rnin., 28sec, A M. Sunday at 
the above meridian. Now we have seen that it is one day 
later immediately west of this line than immediately east of 
it. The time immediately west of this line must, therefore, 
be 2 o'clock, 36 min., 28sec. A M Monday. 

The difference between the 180th. meridian and Sidney is 
the difference between 180 and 151 °, 11' is 28 , 49*, 
which divided by 15 gives ihr., 55mm., i6sec. ; but since 
Sidney is west of the 1 80th meridian, it will be ihr., 55mm., 
16 sec. earlier at the former than at the latter place, which 
time is the differance between 2hr ., 36mm. , 28sec.,and ihr., 
55min., i6sec, which is equal to 41mm., and I2sec, 
A M, Monday. Ans. 

Can you solve this problem by going east from Honolulu? 
If you can, do so . 



LESSON XV. 



1. Projections. — The term projection means the dif- 
ferent methods of drawing maps. 



ASTRONOMICAL GEOGRAPHY. 57 

2. Maps. A Map is a drawing representing the whole 
or part of the earth's surface. 

3. Mercators Projection. — Mercator's Projection 
represents the parallels and meridians as straight lines. The 
region around the poles are made to appear much larger in 
an eastern and western direction than they really are. It is 
therefore, not a true representation of the earth's surface, 
but as they show relative positions correctly, Mercator's pro- 
jections are used by navigators and also in physical geogra- 
phies. 

4. Orthographic Projections. — An Orthographic 
Projection represents the earth's surface as it would appear 
to an observer viewing it at a great distance from the earth. 

5. Stereographic Projections. — A Stereographic 
projection represents the earth's surface as it would appear 
to an observer standing on the earth. 

There are two stereographic projections used more fre- 
quently than others, the Equatorial and the Polar. 

An Equatorial Projection is one in which the equator is 
taken as the center. 

A Polar Projection is one in which one of the poles is 
taken as the center. 

A Concave Projection is one used to represent a small 
portion of the earth's surface, as a State. 

6. Directions- — In all maps the top represents north ; 



58 ASTRONOMICAL GEOGRAPHY. 

the right side east ; ihe bottom south ; and the left side 
west . 

7. Hemispheres. — A hemisphere is half a sphere. 
The equator divides the earth into a Northern and Southern 
Hemisphere. The 20th meridian west and the 160th mer- 
idian east of Greenwich divide the earth into an Eastern 
and Western Hemisphere . 

A great circle can also be passed through the Earth so 
dividing it into two parts that nearly all the water will be in 
one part and the land in the other. The first is called the 
Water Hemisphere and the second the Land Hemisphere. 

The pole or center of the land hemisphere is near Lon- 
don, England, while the center of the water hemisphere is 
near the island of New Zealand. 



LESSON XVI. 



I. Day and Night. — Day and Night are caused by the 
rotation of the Earth on its axis . The side of the Earth 
turned towards the Sun is lit up, and it is day on that por- 
tion, while the opposite side is turned away from the Sun 
and lies hidden in its own shadow, and, hence, it is night on 
the non-illuminated portion . 

As the Earth rotates it presents all of its parts to the Sun, 
hence, all parts of the Earth have day and night. 



ASTRONOMICAL GEOGRAPHY. 59 

2. The Great Circle of Illumination. — The line 
which separates the illuminated from the non-illuminated 
parts of the Earth is the circumference of a great circle and 
is called the Great Circle of Illumination. 

3. The Shape of the Earth's Shadow. — The shape of 
the Earth's shadow is that of an immense cone with its base 
on the Earth and its apex about 850,000 miles distant. 

4. Length of Days. — The rotation of the Earth also 
causes the stars to rise in the east and set in the west ; but 
on account of th§ Earth's yearly motion, the time that elapses 
from the time a star passes a meridian until it passes it again 
is not as great as the time that intervenes between one pass- 
age of the Sun over the same meridian and the next. 

The time that elapses from one noon till the next noon is 
called the Solar Day. The length of the solar day varies ; 
its mean length is 24hrs. 

The exact time that it takes the Earth to make one rota- 
tion or the time that intervenes between two successive pass- 
ages of a star over a given meridian is called the Sidereal 
Day. It is 23hrs. 56mm. 4sec. long. 

5 . Difference Between the Sidereal and Solar 
Day Explained. — In Fig. 8, S represents the Sun ; 1 rep- 
resents the earth with the Sun over the meridian A. Now 
the earth travels along in its orbit from 1 to 2 in a sidereal 
da)' and changes its position with respect to the Sun, but on 
account of the enormous distance to a fixed star, no change 



60 



ASTRONOMICAL GEOGRAPHY. 



in position will be noticed with respect to one oi these bod- 
ies, and hence, as a fixed star will appear over a meridian 
every time the earth makes one rotation. When the star is 




Fig. 8. 



over A in 2, the Sun has not yet arrived over that point, but 
is directly over the meridian C. Therefore, the Sun will be 
behind the star by exactly the time it takes the earth to 
rotate from A to C, 



LESSON XVIL 



i. The Earth's Revolution. — Before discussing the 
variation of the solar day we must thoroughly understand 
the motion of the earth in its orbit. We have seen, Kep- 
ler's First Law, that the earth describes an eliptical orbit 



ASTRONOMICAL GEOGRAPHY. 61 

around the Sun and that the center of the Sun occupies 
one of the foci of the elipse. Since this is not the 
center, the earth is not the same distance from the Sun in 
all parts of its orbit* 

When the earth is in that part of its orbit nearest the 
Sun, it is said to be at Perihelion (Greek, peri, near and 
Helios, Sun) . When it is in that part of its orbit which is 
farthest from the Sun it is said to be at its aphelion (Greek, 
apo,fromand Helios, Sun), The earth's perihelion distance 
is about 90,000,000 miles while its aphelion is 93,000,000 
miles. The Earth's orbit is 577,000,0,00 miles in extent. 
The earth does not travel the same rate at all times, but 
moves faster at perihelion than at aphelion . Its mean ve- 
locity is about 19 miles per second or 1,500 times faster than 
a fast railroad train . 

The relative rate of the earth's revolution is concisely ex- 
pressed in what is known as Kepler's Second Law, which 
is as follows : 

The radius-vector of a planet sweeps over equal areas in 
equal times. By the radius*vector of a planet, we mean 
the line connecting that planet and the Sun, 

In fig. 9 suppose the Sun at S, and the Earth at C ; the 
line C S is the radius-vector . Now suppose the Earth to 
travel from C to D in a certain period of time (say one 
month,) the radius-vector will have described the area CS D, 
Now, it is evident that when the Earth is nearest the Sun 



62 



ASTRONOMICAL GEOGRAPHY: 



and the radius-vector, therefore, shortest, that it must travel 
fastest to describe an equal area in an equal time. Thus 
F E is greater than D C, while A B is greater than F E, 
but the areas, S A B, S E F and SDC are all equal, each 
being described in one month . 







^Sw^ 










/diiiiiP^ 






a/ 


lk§^l_ 






\n 


oEss^HKBl 


■■■ 


^(J 


bT 











Fig. 9. 

2. Cause of the Variation of the Solar Days. — - 
It may be seen from Fig. 8., that the faster the earth travels 
in its orbit, the greater will be the the arc A C, and hence, 
the longer the solar day. Again the slower the earth trav- 
els, the shorter will be the arc A C and therefore, the shorter 
the solar day. 

Therefore, the difference in the rate of travel of the 
earth in its orbit is the cause of the varation in length of the 
solar day. 

3. " Equated Time." — Equated Time is true clock 



ASTRONOMICAL GEOGRAPHY. 63 

time. Twenty-four of its hours measure the mean length of 
solar day> This is also called Astronomical Time . 

4. Sun Fast and Sun Slow.— Since a true clock 
measures the time of the mean Sun, it follows that at times 
it must be behind, and at other times ahead of true or Sun 
time. Now when the earth travels in its crbit faster than 
its mean rate, it will be seen by consulting Fig. 8, that it 
takes longer for the Sun to come to the meridian A, hence, 
the Sun is behind the clock and it is said to be slow. 

When the earth travels in its orbit slower than its mean 
rate, the Sun arrives over the meridian A before the clock 
indicates noon, and hence, Sun time is in advance of the 
clock and the Sun is said to be fast. 

From December 24th, to April 15th, the Sun is slow. 
From April 15th to June 15th, the Sun is fast. From June 
15th, to September 1st, the Sun is slow. 

From September 1st, to December 24th. the Sun is fast. 
At the above dates the equated and true time are the same. 

5. Equation of Time. — The Equation of Time is the 
difference between the true solar day and the mean solar 
day. Thus on February nth, the Sun is 14^ minutes be- 
hind the clock and the equation of time is written plus 14}^, 
because it must be added to the time shown by a sun-dial to 
make it correspond to the time shown by a correct clock. 

On May 14th, the Sun is 4 minutes fast, and the equation 
of time is written — 4, because it must be subtracted from 



64 ASTRONOMICAL GEOGRAPHY. 

Sun time to make it correspond to equated or clock time . 
On July 25th, the equation of time is plus 6 ; on November 
1st minus 165^. 



LESSON XVIII. 



1. The Zodiac. — By consulting Fig. 8 5 we see that if a 
fixed star and the Sun are together when the earth is at 1, 
they will not be together when the earth is at 2, but, on the 
other hand, the Sun will be to the east of the fixed star. 
As the earth progresses in its orbit, the Sun continues to 
move eastward among the stars until it makes one apparent 
revolution in the heavens. This zone or belt is called the 
Zodiac and is about 9 wide. The Zodiac is divided into 12 
equal parts each part being called a Sign. Each sign, 
therefore, contains one twelfth of 360 or 30 . 

The Earth moves through one twelfth of its orbit every 
month and hence, the Sun appears to move through a sign 
of the Zodiac every month . In the Zodiac may be found 
the Sun and major planets, also 12 constellations of stars 
named as follows : 

Aries, the Ram. 

Taurus, the Bull. 

Gemini, the Twins. 

Cancer, the Crab. 



ASTRONOMICAL GEOGRAPHY. 65 

Leo, the Lion, 

Virgo, the Virgin* 

Libra, the Balance . 

Scorpio, the Scorpion, 

Sagittarius, the Archer. 

Capricornus, the Goat. 

Acquarius, the Water-bearer. 

Pisces, the Fish. 
They must not be confounded with the signs of the Zo- 
diac of the same name and should be learned in the order 
named above. Since the stars make one more apparent 
revolution around the Earth than the Sun, every year, it fol- 
lows that in a year of 365 days, the Earth makes 366 rev- 
olutions. 

2. Length of Different Years Explained . — The exact 
time that it takes the Earth to make one revolution is called 
the Sidereal Year. It is the time from one meeting of the 
Sun and a fixed star in the Zodiac until the next. Its length 
is 365 days, 6 hours, 9 minutes, and 9.6 seconds. 

The attraction of the Sun on the equatorial protuberance 
of the Earth tending to make our planet settle down per- 
pendicular to the plane of the ecliptic, causes the Earth's 
equator to meet the plane of the ecliptic before it makes 
one complete revolution ; hence, the places where the 
equator crosses the plane of the ecliptic precede those 
places where it would cross this plane if the' Earth were a 



66 ASTRONOMICAL GEOGRAPHY. 

a perfect sphere ; hence, this motion of the earth is termed 
the Precession of the Equinoxes. This is called the Trop- 
ical Year, and is the time from one vernal equinox to the 
next. It measures 365 days, 5 hours, 48 minutes and 46.05 
seconds. Again we may take the time from one perihe- 
lion to the next ; this is called the Anomalistic Year. 

Now if the Earth's aphelion and perihelion points were 
stationary, there would be no difference between the anom- 
alistic and the sidereal year, but these points are constantly 
moving forward making a complete revolution in 21,000 
years ; hence, it takes longer for the Earth to travel from 
one perihelion to the next than it does to make one revolu- 
tion. The anomalistic year measures 365 days, 6 hours 13 
minutes, 49 seconds. At present we are at perihelion Jan- 
urary 1st. In about 4,600 years perihelion and the vernal 
equinox will correspond. 

3. Effect of the Change of Aphelion and Perihelion— 
Since we are in perihelion Janurary 1st., we are 3,000,000 
miles nearer the Sun in winter, north of the equator, than 
in summer, while we are 3,000,000 miles nearer the Sun, 
south of the equator, in summer than in winter. This dif- 
ference so intensifies the solar heat that Australia and other 
places in the southern hemisphere have a higher tempera- 
ture than places of a corresponding latitude in the northern 
hemisphere. About 10,000 years ago the reverse must have 



ASTRONOMICAL GEOGRAPHY, 67 

been true, the Earth being at perihelion at the time of our 
northern summer. 

4. Effkct of the Precession of the Equinoxes. — It is 
evident that the Earth's axis changes its direction on account 
of the precession. 

The axis revolves around a. point in the heavens in 25,870 
years ; hence, the north star of to-day will not be the north 
star several thousand years from now. 



LESSON XIX, 



The Change of Seasons. — The Change of Seasons is 
caused by the revolution of the Earth together with the in- 
clination of its axis and the constant parallelism of its axis. 

First,— The inclination of the Earth's axis to a perpen- 
dicular to the plane of the ecliptic is nearly 23^° (exactly 
23 27' 24"). 

Second, — The Earth's axis always points in the same di- 
rection, namely, towards the north star ; hence, it matters not 
in what part of its orbit the Earth may be, its axis is always 
parallel to any former position. 

Now the more nearly perpendicular the Sun's rays fall 
upon the earth, the more heat they produce, and since only 
one-half of the Earth is illuminated at a time, the point 



68 



ASTRONOMICAL GEOGRAPHY. 



where the Sun's vertical rays reach the Earth, is the pole of 
the illuminated portion* 

A and B in figure 10 represent 
the Earth at perihelion and ap- 
helion. The south pole is now 
, turned towards the Sun, and its 
. rays fall perpendicular on the 
Tropic of Capricorn . We now 
have summer in the southern hem- 
isphere, while in the northern 
| hemisphere which receives the ob- 
lique rays, it is winter. When 
the Earth is at B or aphelion, the 
Sun's rays fall perpendicular upon 
the Tropic of Cancer. The north- 
ern hemisphere is now turned to- 
ward the Sun and we have sum- 
mer north of the equator and win- 
ter south of it. 

On the 2 2d. of March and again 
on the 2 2d. of September, the 
Sun's rays fall perpendicular upon 

Fig. 10. 

the equator ; at the former we have autumn in the southern 
hemisphere and spring in the northern ; at the latter, we 
have spring in the southern and autumn in northern hemis- 
phere . We now see that the three circumstances mention- 




ASTRONOMICAL GEOGRAPHY. 69 

ed at the beginning of this paragraph, all play an important 
part in producing the change of seasons, for if either the in- 
clination, parallelism of its axis, or the revolution of the 
Earth was wanting, different portions of the earth would not be 
constantly turning towards the Sun, and hence, there would 
be no cause to which the change of seasons could be attrib- 
uted. 

At the equator the days and nights are always of an 
equal length, (12 hours each.) 

On the 22d, of March as we have already seen, the Sun's 
rays fall perpendicular upon the equator, and the oblique 
rays must, therefore, just reach the poles, hence, the days 
and nights are an equal length all over the Earth. 

This is called the Vernal Equinox (Latin aequus, equal 
and nox, night). As the^earth moves forward in its orbit, 
it gradually presents the northern hemisphere to the Sun, 
and its vertical rays reach higher latitudes every day. The 
rays must, therefore, reach places beyond the north pole, and 
in spite of the Earth's rotation, the Sun does not set at that 
place, and it is perpetual day, while the south pole is left 
in utter darkness. The Sun's vertical rays continue to re- 
cede from the equator until June 21st, when they cease. 
The earth is then near aphelion and the Sun's vertical rays 
fall upon the tropic of cancer. This is called the Summer 
Solstice (Latin, Sol, the Sun, and stare, to stand ; so named 
because the Sun upon reaching his northern and southern 



70 ASTRONOMICAL GEOGRAPHY. 

limits seems to be stationary a short time in the heavens) 
and is the point where the Sun's vertical rays stop receding 
from the equator. Since the Sun's vertical rays now fall 
23^ ° north of the equator, it follows that it rays also reach 
23^° beyond the north pole, or to the artic circle. From 
June 2 1st the Sun's vertical rays again approach the equator 
until they once more fall upon that circle. This they do on 
the 22d of September and we then have the Autumnal 
Equinox . 

All this time the north pole has been exposed to sunlight, 
hence, we see that at this place day lasts six months . Twi- 
light now lasts about a month then all is dark and cold. 

From the autumnal equinox the Sun's vertical rays again 
recede from the equator into the southern hemisphere until 
the 2 1 st of December when they fall upon the tropic of 
Capricorn . The Sun has now reached the Winter Solstice, 
and his rays pass over the south pole to the antarctic circle. 
The south pole now has perpetual day and the north pole 
one continued night . The Sun at this time is near perihel- 
ion and it at once reapproaches the equator, reaching that 
place on the 22nd of March, when it recommences a tropical 
year. 



LESSON XX. 



1. Zones. — A zone is a division of the Earth. Of these 



ASTRONOMICAL GEOGRAPHY. 71 

there are three principal kinds, namely,Mathematical, Phys- 
ical and Zones of Time . 

2. Mathematical Zones. — The Earth is divided into 
five mathematical or astronmical zones. They are bounded 
by the tropics and the polar circles. 

3. The Frigid Zones. — The Frigid Zones lie between 
the polar circles and the poles. The one which surrounds 
the north pole is called the North Frigid, the one which 
surrounds the south pole the South Frigid. 

4. The Temperate Zones. — The Temperate Zones lie 
between the tropics and the polar circles . The one north of 
the equator is called the North Temperate, the one south of 
the equator is called the South Temperate Zone. 

5. The Torrid Zone. — The Torrid Zone is that belt of 
the Earth included between the tropics. The Sun's rays 
fall perpendicular upon one part or other of this zone every 
day of the year. 

6. Width of the Zones. — The width of the Zones is 
as follows : Frigid 23^° ; Temperate 43 ° ; Torrid 46 . 

The width of a zone depends upon the inclination of the 
axis of the planet it surrounds. If the Earth's axis were 
inclined 30 , instead of 23^°, the frigid zones would each 
be 30° ; the torrid 6o° ; and each of the temperate 30 wide. 

7. Physical Zones. — Physical Zones are bounded by 
lines drawn through places having the same mean annual 
temperature . These lines are called Isothermal Lines . 



72 ASTRONOMICAL GEOGRAPHY, 

8. Zones of Time. — in order to avoid confusion of 
time in travelling from east to west or from west to east, 
railroad men have divided the Earth into 24 Zones ; each 
Zone is, therefore, one twenty-fourth of 360 or 15 wide. 
All places situated within any one Zone are made to have 
the same time, it being the time of a certain meridian of that 
Zone . This is called Railroad or Standard Time. 

The following meridians are used : o° is called Univer- 
sal time ; West 15 , West African ; 30 , Central Atlantic ; 
45 , East Brazilian ; 60 °, La Plata ; 75 ° Eastern ; 90 , 
Central ; 105 , Mountain ; 120 , Pacific ; 135 , East Alas- 
kan ; 150 , Central Alaskan ; 165 , West Alaskan ; 180 , 
Transitional; East 165 , is called New Caledonian ; 150 , 
East Australian ; 135 , Corean ; 120 , East Asia ; 105°, 
Siam ; 90 , East Hindostan ; 75 , West Hindostan ; 6o c> , 
Ural ; 45°, Caucasus; 30 , Bosporus; 15 , Scandinavian. 

9. Length of Day and Night. — When the Sun's ver- 
tical rays fall in either hemisphere, it is evident that more 
than one half of it will be illuminated, and the day will ex- 
ceed the night in the proportion that the illuminated part of 
a parallel exceeds the ncn-illuminated part. 

Since the Sun's rays at times pass over the poles to the 
polar circles, it follows that day in the frigid zones may ex- 
ceed one complete rotation of the Earth. The following re- 
ference table exhibits the length of the longest day in the 
given latitudes. 



ASTRONOMICAL GEOGRAPHY. 73 



Latitude. 



Equator — 
Tropics 

30 Degrees . 

40 

50 

60 

Polar Circles . 

67^ « 

69K " 

73.3 " 

78.3 " 

84 

Poles 



Greatest Length of Day or Night. 



12 hours 

13.5 *' 

14 

15 

16.3 " 

18.7 " 

24 " 

1 month 

2 

3 

4 

5 

6 



io , Altitude . — By the altitude of a heavenly body we 
mean its distance in degrees above the horizon. Since the 
distance from the horizon to the Zenith is one fourth of a 
circle, the greatest altitude a body can have is 90 degrees. 

Let us suppose you were standing on the north pole at 
the time of the vernal equinox ; you would see the Sun at 
the horizon, and his altitude would then be zero ; but sup- 
pose you travel to the south ; then for every degeee you 
travel, the Sun's altitude increases one degree . Suppose 
you travel to Columbus, Ohio, which is in 40 north latitude ; 
you will have traveled 90° minus 40 equals 50 , and hence 
the altitude of the Sun at Columbus on 2 2d of March is 

50 . 

What is the Sun's altitude on 21st of June ? Since the 
Sun appears to move north 23^° from the March equinox 
till the 2 1 st of June, the Sun's altitude must be 50^ plus 23^° 
equals 73 %° . Since the Sun appears to move south from 
the September equinox till the 21st of December, his altit- 



74 ASTRONOMICAL GEOGRAPHY. 

tude at Columbus on the later date must be 50 minus 23^° 
equals 26^°. 

What will be the Sun's altitude at Columbus May 1st? 

Since the Sun travels north from March 2 2nd to June 2ist, 
23^2 degrees in 91 days, he will travel-^- divided by 91 
equals ~^° in one day. The time from the vernal equinox 
to May 1st, is ao days. Hence the Sun will have increased 
his altitude ^L° x 40 equals io-f£°. 

Therefore, his altitude at Columbus is 50 plus 
to »° equals 60- 3 ?- . 

91 ^L 91 

1 1 . What Next ? My Dear Students ; — Our work 
is now finished. For some time we have enjoyed each 
others company and drank from the same cup of knowledge. 
Our minds have penetrated into the mighty depth of space 
and visited the wonders of the heavens. Trusting that by 
our voyage, we have all been strengthened in our grateful- 
ness to the Great Master Mind of Creation ; that we may 
go forth into the world and make strong, pure, and noble 
men and women; and that we may meet again in new fields, 
to explore the works of Nature, I bid you all Farewell. 

THE END. 



Corrections. — Opogee on page 30 should be apogee, 
[LESSON VIII,] page 23 should be [LESSON XVIII.J 



CONTENTS. 

INTRODUCTION . 

PAGE. 

Derivation .... 5 

Sphere of Geography . . . .5 

Classification ..... 6 

Mathematical Definitions . . . .7 

LESSON II. 

The Universe . . . . 11 

Constitutents of the Universe . . . .11 

Nebulae . . . . .11 

Stars . . . . . .12 

Magnitude . . . . .14 

Constellations . . . . 14 

Variations . . . . . . 14 

Color ... . . . .15 

Constituents of the Stars . . . .15 

The Milky Way . . . . .15 

LESSON III. 

The Solar System . . . .16 



76 ASTRONOMICAL GEOGRAPHY 

Constituents . ... 



The Sun 

Planets 
Mercury 
Venus 
Mars 



LESSON IV, 



LESSON V, 



Jupiter 

Saturn 

Uranus . 

Neptune 

The Planets in General 

LESSON VL 

The Asteroids 

Satellites 

Laplace's Nebular Hypothesis , 

LESSON VIL 

The Moon 

The Moon's Phases 

Eclipses 

Effects of Eclipses upon the Ignorant 



16 
16 

x 9 

l 9 
20 

23 

22 

23 
24 

25 
26 



26 

27 
27 



30 

31 

33 
34 



ASTRONOMICAL GEOGRAPHY. 77 
LESSON VIII. 

Comets ..... 34 

Effects of Comets upon the Ignorant , . 35 

Meteors 3 6 

The Zodiacal Light . , * . * 38 

LESSON IX, 

The Earth ..... 38 

Law of Inertia . . 38 

Law of Universal Gravitation > . 40 

Newton's Second Law of Motion . * * 41 

LESSON X. 

Motions of the Earth ...» 42 

Cause of the Earth's Revolution . * ,42 

Proofs that the Earth Revolves » * 44 

LESSON XL 

Cause of the Earth's Revolution * > . 44 

Proofs that the Earth Rotates . . . 45 

Shape of the Earth . > . . .46 

Proofs that the Earth is round > . .46 

LESSON XII. 

Dimensions and Density of the Earth , * 48 

Cause of the Earth's Oblateness . . 48 

Does the Mississippi River Run up Hill k » 48 



78 ASTRONOMICAL GEOGRAPHY. 

Why some Rivers Run up Hill . . 49 

Points . . . . . . , 49 

LESSON XIII. 

Imaginary Lines . . . . 50 

Latitude . . . . . 51 

Longitude . . . . . 5 2 

Value of Degrees of Latitude . . • 53 

Value of Degrees of Longitude . . 53 

LESSON XIV. 

Longitude and Time . ... 54 

International Date Line . . . 55 

Time Varies . . . . -55 

Problem . . . . -55 

Solution . . . • 56 

LESSON XV. 

Projections . . . . . 5^ 

Maps . . . . -. .57 

Mercator's Projection 57 

Orthographic Projections . . - . -57 

Stereographic Projections . . . 57 

Directions . . . . . -57 

Hemispheres . . . . . 5^ 

LESSON XVI. 

Day and Night . . . . 5 8 



ASTRONOMICAL GEOGRAPHY. 79 

The Great Circle of Illumination . . 59 

The Shape of the Earth's Shadow . . -59 

Length of Days . . » 59 
Difference between the Sidereal and Solar Day Explained 59 

JLESSON XVIL 

The Earth Revolution . . . .60 

Kepler's Second Law . . . » 27 

Cause of the Varation of the Solar Days . . 62 

" Equated Time "' ... .62 

Sun Fast and Sun Slow . . . 63 

Equation of Time . . . * 63 

LESSON XVI1L 

The Zodiac . . * 64 

Length of different Years Explained . ■. 65 
Effects of the Change of Aphelion and Perihelion , 66 

Effects of the Precession of the Equinoxes . . 67 

LESSON XIX. 

The Change of Seasons * . > -67 

LESSON XX 

Zones . 70 

Mathematical Zones . . . . 71 

The Frigid Zones - - * 7 1 



80 ASTRONOMICAL GEOGRAPHY* 

The Temperate Zones - - - 71 

The Torrid Zone - • - - -71 

Width of Zones - - - 71 

Physical Zones - - - - - 71 

Zones of Time - - - - 72 

Length of Day and Night - - -. 7 2 

Altitude ---- 73 

Corrections - - - - 74 

What Next ? - - - - 74 

Contents - - 75 



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A Copy of the Astronomical Geography will be sent 
post-paid to any address on receipt of 75 cents. 

S. M. SARK, 

Circleville, Ohio. 



